In a larger bowl, beat the butter and sugar together until light and fluffy.
Add the eggs and vanilla and mix well.
Add the mashed banana and mix well.
In a separate bowl, mix together the flour, baking powder and baking soda.
Add the flour mixture gradually to the large bowl, stirring well.
Gently stir in the chocolate chips and buttermilk.
Pour the mixture in to a greased and lined 10x12 inch baking tray. Put in a preheated oven at 190°C/375°F/Gas 5 for 50 minutes, until a knife comes out clear.
To make the frosting, mix together the cream cheese and mascarpone. Then gradually add the icing sugar and the vanilla and mix well.
Once the cake it cooked, remove it from the oven and pan and put on a cooling rack and cool for at least an hour. Spread with the frosting and put in the fridge for a couple of hours for the frosting to set.
You could swap the dark chocolate chips for white chocolate chips.
Not a fan of cinnamon? Use ginger or nutmeg, or a mixture of the three.
You could make a chocolate cream frosting by swapping a little of the icing sugar for cocoa powder.
You can make these in to cupcakes by dividing the batter in to cupcake cases until half full and then baking for 22 minutes.
Feel free to get creative with extras like raisins, white chocolate chips or chopped pecans or walnuts.